This invention relates to biodegradable polymers and to methods of making them from non-biodegradable polymers such as petroleum -based plastics combined with other biodegradable polymers, such as for example, carbohydrates, proteins, lipids or the like.
It is known to alter polymers such as petroleum-based plastics by the incorporation of some carbohydrates to increase their biodegradability. One prior art biodegradable polymer and method of making it is disclosed in U.S. Pat. No. 4,016,117 to Griffin, issued Apr. 5, 1977. In this product, a synthetic resin incorporates particles of biodegradable substances and an auto-oxidizable substance. The processing preserves the starch granules in the final product. This polymer, when it contacts a transition metallic salt, auto-oxidizes to generate a peroxide or a hydroperoxide.
Other biodegradable products are disclosed in U.S. Pat. Nos. 4,405,731 to Carter issued Sep. 20, 1983; 3,778,392 to Hughes issued Dec. 11, 1973; 3,949,145 to Otey et al. issued Apr. 6, 1979; and 4,280,920 to Kesting.
The biodegradable plastics disclosed in these United States patents have the disadvantages of only containing from approximately 5 percent to 15 percent carbohydrate while retaining its characteristics as a plastic although they may have up to 50 percent starch but become paperlike at such high levels and lose the typical characteristics of thermoplastic or thermosetting plastics. The altered structure reduces the elasticity and shear strength.